Differing qualification for a UK passport and birth certificate is somewhat more of an quagmire than those other explicitly devolved policies. This isn't like prescriptions or college fees where differing taxation matters. Nor is it based on centuries old legal traditions, like marriage or whatever.
Put it this way, I don't see the cross border constitutional and administrative headaches this throws up as being remotely simple, nor capable of being wished away. The powers of devolved administrations to affect the specifics of equalities legislation are, I would have thought, something that needs to be resolved carefully by the UK as a whole- the clue is in the name. Differences either side of the border may suit short term political ambitions but isn't realistic in the longer run. Obviously, if Scotland gains independence it can do what it likes, or what its politicians like, but until then I think its inevitable that Westminster will squash this.